1. Field of the Invention
This invention relates to an apparatus for processing workpieces, particularly superimposed workpieces, comprising a table having a supporting surface, means for fixing the workpieces to the supporting surface, and a numerically controlled tool unit, which is movable over the supporting surface.
2. Description of the Prior Art
For a joint processing of workpieces which are superimposed in a plurality of layers, for instance, for cutting blanks out of metal plates and for drilling such blanks, or for a cutting of non-adherent materials, such as prepreg materials covered with films on both sides, it is necessary to hold the stacks of workpieces properly relative to the supporting surface and relative to each other. This has been done by screwing or riveting the stacks of workpieces to a fixing pallet, and the fixing pallet is then fixed to the table by the fixing means, which may comprise holding-down claws, suction boxes cooperating with the supporting surface, or other suitable means. For a processing of layers of strip material the layers of each stack are held together by adhesive films and are fixed to a vacuum deck. For a processing of aluminum plates it has been proposed to hold the plates of the stack together by deep-freezing. All these known measures are rather expensive and time-consuming and require the use of auxiliary materials and in some cases require the workpieces to be altered, e.g., perforated. Besides, said known methods must specifically be adapted to the nature of the workpieces and to the methods for processing them.